U.S. patent application number 10/543995 was filed with the patent office on 2006-10-19 for organic optoelectronic device.
This patent application is currently assigned to Cambridge Display Technology Limited. Invention is credited to Julian Carter.
Application Number | 20060231844 10/543995 |
Document ID | / |
Family ID | 9952418 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060231844 |
Kind Code |
A1 |
Carter; Julian |
October 19, 2006 |
Organic optoelectronic device
Abstract
An organic optoelectronic device includes a substrate having an
upper surface and a lower surface, at least one organic diode
situated on the upper surface of the substrate, the organic diode
including, an anode including a material of high work function
situated over the upper surface of the substrate, an organic
optoelectronic material at least partially overlaying the anode, a
cathode including a material of low work function at least
partially overlaying the organic optoelectronic material, the
cathode being transparent or semi-transparent, wherein the
substrate includes at least one connecting via extending through
the substrate from the lower surface to the upper surface, the
connecting via being suitable for providing an electrical
connection between at least one of the anode and/or the cathode of
the organic diode and an external circuit. The invention has
application in organic light emitting devices and organic
photovoltaic devices.
Inventors: |
Carter; Julian;
(Cambridgeshire, GB) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
233 S. WACKER DRIVE, SUITE 6300
SEARS TOWER
CHICAGO
IL
60606
US
|
Assignee: |
Cambridge Display Technology
Limited
|
Family ID: |
9952418 |
Appl. No.: |
10/543995 |
Filed: |
January 29, 2004 |
PCT Filed: |
January 29, 2004 |
PCT NO: |
PCT/GB04/00380 |
371 Date: |
November 21, 2005 |
Current U.S.
Class: |
257/79 |
Current CPC
Class: |
H01L 51/0038 20130101;
H01L 27/3288 20130101; H01L 51/0037 20130101; H01L 51/0036
20130101; H01L 27/3293 20130101; H01L 51/007 20130101; H01L 51/0059
20130101; H01L 51/5234 20130101; H01L 51/0081 20130101; H01L
51/0039 20130101 |
Class at
Publication: |
257/079 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2003 |
GB |
0302550.9 |
Claims
1. An organic optoelectronic device comprising; a substrate having
an upper surface and a lower surface, and at least one organic
diode situated on said upper surface of said substrate, said
organic diode comprising; an anode comprising a material of high
work function situated over said upper surface of said substrate,
an organic optoelectronic material at least partially overlying
said anode, a cathode comprising a material of low work function at
least partially overlying said organic optoelectronic material,
said cathode being transparent or semi-transparent, wherein said
substrate comprises at least one connecting via extending through
said substrate from said lower surface to said upper surface, said
connecting via being suitable for providing an electrical
connection between at least one of said anode and said cathode of
said organic diode and an external circuit.
2. An organic optoelectronic device according to claim 1 wherein
said substrate comprises a ceramic.
3. An organic optoelectronic device according to claim 1 wherein
said substrate comprises a plastic.
4. An organic optoelectronic device according to claim 1 wherein
said organic optoelectronic material comprises light emitting
polymer.
5. An organic optoelectronic device according to claim 1 wherein
said organic optoelectronic material comprises an organic electron
donor and an organic electron acceptor.
6. An organic optoelectronic device according to claim 5 wherein at
least one of said organic electron donor or said organic electron
acceptor comprises a semiconductive polymer.
7. An organic optoelectronic device according to claim 1 wherein
said cathode comprises a thin layer of metal of low work function
in proximity to said organic optoelectronic material and a further
layer of conducting material over said thin layer of metal of low
work function.
8. An organic optoelectronic device according to claim 7 wherein
said thin layer of metal comprises a metal selected from the group
consisting of Ca, Ba, MgAl, LiAl, Mg, and MgAg.
9. An organic optoelectronic device according to claim 7 wherein
said cathode further comprises a layer of insulating material
positioned between said thin layer of metal of low work function
and said organic optoelectronic material, said insulating material
being sufficiently thin to allow the passage of charge carriers
between the low work function electrode and the organic
optoelectronic material.
10. An organic optoelectronic device according to claim 7 wherein
said further layer of conducting material is selected from the
group consisting of ITO, Al, Au, Ag, IZO, and ZnS.
11. An organic optoelectronic device according to claim 1 wherein
said anode is selected from the group consisting of ITO, Au, and
Pt.
12. An organic optoelectronic device according to claim 1 wherein
said device further comprises a layer of passivating material over
said cathode.
13. An organic optoelectronic. device according to claim 1 wherein
said device comprises a plurality of connecting vias extending
through said substrate from said lower surface to said upper
surface.
14. An organic optoelectronic device according to claim 1 or claim
13 wherein said connecting via is at least partially filled with an
electrically conducting material.
15. An organic optoelectronic device according to claim 14 wherein
said electrically conducting material is selected from the group
consisting of highly conductive metals and conductive pastes.
16. An organic optoelectronic device according to claim 1
comprising a plurality of organic diodes.
17. A display device comprising; an organic optoelectronic device
comprising; a substrate having an upper surface and a lower
surface, and, at least one organic diode situated on said upper
surface of said substrate, said organic diode comprising; an anode
comprising a material of high work function situated over said
upper surface of said substrate, an organic optoelectronic material
at least partially overlying said anode, a cathode comprising a
material of low work function at least partially overlying said
organic optoelectronic material, said cathode.being transparent or
semi-transparent, wherein said substrate comprises at least one
connecting via extending through said substrate from said lower
surface to said upper surface, at least one said connecting via
being at least partially filled with an electrically conducting
material, said display device further comprising drive circuitry,
said drive circuitry electrically connected to at least one of said
anode or said cathode through said connecting via or vias.
18. A display device according to claim 17 wherein said drive
circuitry is electrically connected to both said anode and said
cathode through said connecting via or vias.
19. A method of preparing an organic optoelectronic device
according to claim 1 comprising; providing a substrate having an
upper surface and a lower surface, said substrate further
comprising at least one connecting via extending through said
substrate from said lower surface to said upper surface, said
connecting via or vias being at least partially filled with an
electrically conducting material suitable for enabling an
electrical contact to be made between said upper surface of said
substrate and said lower surface of said substrate, providing a
layer of material of high work function over said upper surface of
said substrate, providing a layer of an organic optoelectronic
material over said layer of material of high work function, and
providing a layer of transparent or semi-transparent material of
low work function over said layer of organic optoelectronic
material.
20. A method of preparing an organic optoelectronic device
according to claim 19 wherein prior to providing said layer of
material of low work function said organic optoelectronic material
is removed from above at least one of said connecting vias allowing
said layer of material of low work function to be deposited over
and in electrical contact with said connecting via or said
connecting vias.
21. A method of preparing an organic optoelectronic device
according to claim 19 wherein said organic optoelectronic material
is provided by means of a selective deposition technique such that
said organic optoelectronic material is not deposited over all of
said connecting via or vias such that in said step of providing a
layer of material of low work function said layer of material of
low work function is deposited over and in electrical contact with
said connecting via or said connecting vias.
22. An organic optoelectronic device according to claim 15 wherein
said electrically conducting material is selected from the group
consisting of gold, platinum, aluminum, silver pastes, and graphite
pastes.
23. An organic optoelectronic device according to claim 13 wherein
at least one of said plurality of connecting vias is at least
partially filled with an electronically conducting material.
24. An organic optoelectronic device according to claim 23 wherein
said electrically conducting material is selected from the group
consisting of highly conductive metals and conductive pastes.
25. An organic optoelectronic device according to claim 24 wherein
said electrically conducting material is selected from the group
consisting of gold, platinum, aluminum, silver pastes, and graphite
pastes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic optoelectronic
device, a display device comprising said organic optoelectronic
device and a method of preparing said organic optoelectronic
device.
[0003] 2. Brief Description of the Prior Art
[0004] The past decade has seen an increasing amount of research
into the use of organic materials in optoelectronic devices,
examples of such devices include organic electroluminescent
devices, as disclosed in WO90/13148 and organic photovoltaic
devices, as disclosed in U.S. Pat. No. 5,670,791. Both organic
electroluminescent devices and organic photovoltaic devices are
organic diodes comprising a layer of organic material between two
electrodes. Organic electroluminescent devices emit light on the
passage of a current between the two electrodes. Organic
photovoltaic devices generate a current between the two electrodes
when light is incident upon the device.
[0005] To provide current to drive the organic electroluminescent
devices and to enable charge generated on organic photovoltaic
devices to be conducted elsewhere it is necessary to provide
contacts to the electrodes of the organic diodes. A number of
methods have been developed to provide such contacts. The simplest
method involves the organic diodes being constructed on a single
monolithic substrate such as glass. The lower electrode is situated
on the surface of the substrate, a layer of organic material
overlies the lower electrode with the upper electrode overlying the
layer of organic material. In such a method electrical contacts are
made from the electrodes to the edge of the substrate. The
disadvantage of this method is that where more complex arrangements
of organic diodes are required, as is the case in display
applications, the routing of the electrical contacts becomes
complex and in particular the attachment of driving electronics to
the edge of the substrate may become problematic.
[0006] Organic electroluminescent devices have application in high
information content displays, such displays require a large number
of individually addressable organic electroluminescent devices. To
provide a display comprising a multiplicity of organic
electroluminescent devices on a single monolithic substrate the
devices are generally arranged in the form of a matrix addressed by
a series of rows and columns, the rows and columns having an
orthogonal arrangement. To drive a particular electroluminescent
device a current is driven along the appropriate column with the
appropriate row being grounded, such a display is known as a
passive matrix display. In such passive matrix displays it is
necessary to drive large currents through the electroluminescent
devices since the devices are only addressed intermittently,
typically each device is addressed with a frequency of 50 Hz. The
greater the number of rows and columns in the display the greater
the current which must be provided to each electroluminescent
device. The need to drive a high current through the
electroluminescent devices limits the number of rows and columns
which may be used in such a driving scheme since there is an upper
current limit which may be passed through the organic
electroluminescent device. In order to provide larger displays i.e.
both larger area displays and displays having a greater number of
pixels, it has been proposed to connect several substrates together
to form a tiled display.
[0007] As passive matrix displays on a single monolithic substrate
require contacts to be made to the edge of the substrate displays
of this type are difficult to connect in this manner without the
seams between neighbouring substrates being visible in the eventual
display. An alternative method for providing displays comprising a
multiplicity of organic electroluminescent devices uses a matrix of
switches to address the devices. A switch is positioned at each
electroluminescent device and the devices can be turned on and off
as required without the need to drive a large current through the
device. This method, known as active matrix driving, typically uses
silicon transistors to provide the switching means. A display will
typically be prepared by providing a matrix of switches and other
necessary electronic components formed from low temperature
polysilicon on a substrate which may be glass, this component is
known as the backplane. The organic electroluminescent device will
then be deposited on top of the appropriate switch. This method
overcomes some of the disadvantages of the above discussed passive
matrix method and enables the production of displays having a
greater number of pixels and also displays having a large area. But
such active matrix displays are very complex and expensive to
prepare. Moreover the low yield of the process used to prepare the
active matrix backplanes limits the size of displays which can be
prepared.
[0008] Recently an alternative technology for providing large area
displays which does not have the disadvantages inherent in single
substrate passive matrix displays or active matrix displays has
been developed. This technology uses a ceramic backplane through
which electrically conducting vias are provided. The conducting
vias provide an electrical connection between the electrodes of the
organic diodes and the electronics for driving the display. Since
the conducting vias allow connection to be made to the electrodes
of the device through the middle of the ceramic backplane rather
than at the edges a number of substrates may be seamlessly tiled
together to form a large area display and in this way a large area
passive matrix display may be formed. FIG. 1 shows a method for the
preparation of such a prior art display. FIG. 1a) shows a series of
organic electroluminescent devices 100 on a substrate 101, and a
ceramic backplane 110 which has a number of vias 111 passing from
its upper surface to it's lower surface. The vias are filled with a
conducting material 112 in order to render them conductive. The
component comprising the organic electroluminescent devices
comprises a transparent glass substrate 101, a layer of conducting
ITO (indium tin oxide) patterned to form a series of parallel lines
102 which forms the first electrode, in this case the anode. A
patterned layer of organic electroluminescent material 103 overlays
the ITO. A second electrode, in this case is the cathode 104, is
situated over the organic electroluminescent material. The cathode
is patterned to form a series of parallel lines orthogonal to the
parallel lines of the anode.
[0009] FIG. 1b) shows the prior art display device after bonding of
the ceramic backplane 110 to the component comprising the
electroluminescent devices 100. The ceramic backplane is placed
over the component comprising the electroluminescent devices such
that the conducting vias lie at least partially above the cathodes
of the electroluminescent devices. The conducting vias are then
bonded to the upper electrode of the organic electroluminescent
device in order to provide an electrical contact from the cathode
of the electroluminescent device to the eventual driving circuitry.
The conducting vias are generally bonded to the upper electrode of
the organic electroluminescent device using a conductive paste such
as a silver paste or using a solder 113. The anode 102 may also be
connected to external drive circuitry by means of the vias in the
ceramic backplate. On passing a current through the
electroluminescent devices of the display light is emitted through
the glass substrate. An example of such a prior art display device
is disclosed in WO99/41732.
[0010] Although the above described display devices overcome some
of the problems associated with single substrate passive matrix and
active matrix displays there are a number of disadvantages
associated with these display devices. The displays effectively
comprise two substrates, a front transparent glass substrate and a
ceramic backplane. This increases the complexity of manufacturing
and the thickness and weight of the displays. Further, to provide
an electrical connection to the cathode of the electroluminescent
device, the vias are filled with conductive paste which is
converted to a conductive solid or conductive vias are bonded to
the electroluminescent device using a conductive paste or solder.
The cathode is exposed to the conductive paste or solder and to
solvent vapours generated on converting the paste or solder to a
solid. The cathode of the electroluminescent device is generally
made from a low work function metal such as calcium. Low work
function metals are very sensitive to solvents such as water and so
the filling of the vias degrades the material of the cathode. This
has a deleterious effect on the display, causing defective pixels
(known as black spots) and also reducing the operational lifetime
of the display.
[0011] There is therefore a need to provide an organic
optoelectronic device which combines the advantages associated with
the use of substrates comprising conductive vias but without the
above mentioned disadvantages.
SUMMARY OF THE INVENTION
[0012] The present inventors have developed an organic
optoelectronic device, a display comprising the inventive organic
optoelectronic device and a method for preparing the inventive
organic optoelectronic devices.
[0013] In a first embodiment the present inventors provide an
organic optoelectronic device comprising; [0014] a substrate having
an upper surface and a lower surface, [0015] at least one organic
diode situated on said upper surface of said substrate, said
organic diode comprising; [0016] an anode comprising a material of
high work function situated over said upper surface of said
substrate, [0017] an organic optoelectronic material at least
partially overlying said anode, [0018] a cathode comprising a
material of low work function at least partially overlying said
organic optoelectronic material, said cathode being transparent or
semi-transparent, characterised in that said substrate comprises at
least one connecting via extending through said substrate from said
lower surface to said upper surface, said connecting via being
suitable for providing an electrical connection between at least
one of said anode and/or said cathode of said organic diode and an
external circuit.
[0019] In the organic optoelectronic devices of the present
invention light enters or leaves the device through the cathode
which is transparent or semi-transparent. Where the organic
optoelectronic device is an organic electroluminescent device this
type of device is known as a top emitter. The device architecture
provided by the present invention has the advantage over devices of
the prior art in that the cathode does not come into contact with
the deleterious material used to fill the vias or to bond the
conductive vias to the electroluminescent device. In the devices of
the prior art emission occurs through the transparent anode so to
avoid interfering with the light emission from the display the vias
must contact the other side of the diode i.e. the sensitive
material of the cathode.
[0020] The inventors of the present invention have solved the
problem of deterioration of the cathode material and thereby
provided an organic optoelectronic device having a longer lifetime
and better appearance, in particular with fewer black spots.
[0021] The organic optoelectronic device of the present invention
has a number of additional advantages. Only a single substrate is
used whereas the prior art devices require two substrates i.e. a
glass substrate and a ceramic backplane. The use of a single
substrate leads to lighter and cheaper displays. A corollary of
this is that no registration of two substrates is required in the
manufacturing of the device of the present invention. In the
devices of the prior art such registration steps increase the
complexity of manufacturing and generally require additional
features on the substrate to aid registration. The two substrates
of the prior art devices serve to protect the organic
optoelectronic material and the cathode from the environment. In
the devices of the present invention alternative passivating
materials or barrier layers may be used, these not only enable the
devices to be lighter than those of the prior art but also, where a
suitable substrate is used, enable flexible and/or conformable
devices to be produced.
[0022] The substrate of the present invention may be planar with
the upper and lower surfaces being parallel to one another although
other arrangements in which the substrate is for example convex or
concave are also envisaged.
[0023] The connecting vias may be through holes which pass from one
surface of the substrate to the other and which are suitable for
filling with a conducting material or may be conductive traces or
lines such as metal connectors which form an integral part of the
substrate. Where the connecting vias are formed as an integral part
of the substrate they may provide both a vertical connection
between the upper and lower surfaces of the substrate and also a
lateral connection between different regions of the substrate.
[0024] The organic diodes which form the optoelectronic device of
the present invention are preferably organic electroluminescent
diodes, also known as organic light emitting diodes, or organic
photovoltaic diodes. The organic diodes comprise a layer of organic
optoelectronic material situated between two electrodes, namely an
anode and a cathode.
[0025] In a preferred embodiment said substrate comprises a ceramic
or a plastic material.
[0026] Suitable ceramics may be selected from high temperature
fired ceramics and low temperature co-fired ceramics. Low
temperature co-fired ceramics are preferred.
[0027] Suitable plastics may be selected from polyvinyl chloride,
acrylonitrile butadiene styrene (ABS), aromatic polyimides,
polyimides, propylene, polyphenylene sulfide, polycarbonate,
acrylics, polyesters, polyethylene terephthalate (PET),
polyethylene naphthalate (PEN), polyether sulfone and cyclic
olefins. The substrate may be a single monolithic material or may
comprise layers of the same or different materials. The substrate
may comprise at least a layer of insulating material and at least a
layer of conducting material such as a metal.
[0028] The organic optoelectronic material of the present invention
is an organic material with optical and/or electronic properties.
Such properties include electroluminescence, photoluminescence,
fluorescence, photoconductivity and conductivity.
Electroluminescent materials include light emitting polymers, light
emitting dendrimers and so called small molecules such as aluminum
trisquinoline.
[0029] Photoconductive materials include photoconductive polymers,
photoconductive small molecules and fullerenes (C.sub.60).
[0030] In a preferred embodiment the organic optoelectronic device
is an organic electroluminescent device and the organic
optoelectronic material comprises a light emitting polymer.
Preferred light emitting polymers include polyfluorenes,
polybenzothiazoles, polytriarylamines, poly(phenylenevinylenes) and
polythiophenes.
[0031] In a preferred embodiment the organic optoelectronic device
is an organic photovoltaic device and the organic optoelectronic
material is an organic photoconductor. To provide an organic
photovoltaic device said organic optoelectronic material preferably
comprises an organic electron donor and an organic electron
acceptor. More preferably at least one of said organic electron
donor or said organic electron acceptor comprises a semiconductive
polymer. Suitable organic electron donors and acceptors may be
selected from the group comprising polyfluorenes,
polybenzothiazoles, polytriarylamines, poly(phenylenevinylenes) and
polythiophenes. Particularly suitable organic electron acceptors
include fullerenes, fullerene derivatives and polymers comprising
fullerenes.
[0032] The cathode may comprise a single layer of material or
multiple layers of materials. The cathode may comprise a metal or
an organic material such as a polymer. Preferably the cathode
comprises a thin layer of metal of low work function in proximity
to the organic optoelectronic material and a further layer of
conducting material over said thin layer of metal of low work
function. The thin layer of metal provides electron injection into
or electron collection from the layer of organic optoelectronic
material. The thin layer of metal is preferably selected from the
group comprising Ca, Ba, MgAl, LiAl, Mg or MgAg.
[0033] The further layer of conducting material is preferably a
material which is sufficiently transparent to allow light to enter
or exit the layer of optoelectronic material and is also
sufficiently conductive to allow charge to be driven into or drawn
out of the optoelectronic device. The further layer of conducting
material is preferably selected from the group comprising ITO, Al,
Au, Ag, IZO (indium zinc oxide) or ZnS.
[0034] To improve device efficiency a layer of insulating material
may be provided between the layer of organic optoelectronic
material and the cathode. In such cases the cathode further
comprises a layer of insulating material positioned between said
thin layer of metal of low work function and said organic
optoelectronic material. The insulating material being sufficiently
thin to allow the passage of charge carriers between the low work
function electrode and the organic optoelectronic material. The
thin layer of insulating material preferably has a thickness of
between 1 nm and 10 nm. The insulating material is preferably
selected from the group comprising alkali or alkaline earth metal
fluorides and most preferably is selected from amongst LiF,
BaF.sub.2 and NaF.
[0035] The anode of the organic optoelectronic device is preferably
selected from the group comprising ITO, Au, Pt.
[0036] The anode preferably comprises a material having a work
function of greater than 4.3 eV and the cathode preferably
comprises a material having a work function of less than 3.5
eV.
[0037] To improve the lifetime of the organic optoelectronic device
the device is protected from contact with atmospheric oxygen and
moisture preferably by providing a layer of passivating material
over said cathode. The passivating material forms a barrier
preventing the ingress of oxygen and water vapour.
[0038] In a preferred embodiment said organic optoelectronic device
comprises a plurality of connecting vias extending through said
substrate from said lower surface to said upper surface.
[0039] It is preferred that the connecting via or a at least some
of the plurality of connecting vias are at least partially filled
with an electrically conducting material. The electrically
conducting material may be selected from the group comprising
highly conductive metals such as gold, aluminum or platinum or
conductive pastes such as conductive silver or graphite pastes.
[0040] Preferably the organic optoelectronic device comprises a
plurality of organic diodes, such an arrangement enables the
formation of a high information content display.
[0041] In a further embodiment the present invention provides a
display device comprising; [0042] an organic optoelectronic device
comprising; [0043] a substrate having an upper surface and a lower
surface, [0044] at least one organic diode situated on said upper
surface of said substrate, [0045] said organic diode comprising;
[0046] an anode comprising a material of high work function
situated over said upper surface of said substrate, [0047] an
organic optoelectronic material at least partially overlying said
anode, [0048] a cathode comprising a material of low work function
at least partially overlying said organic optoelectronic material,
said cathode being transparent or semi-transparent, characterised
in that said substrate comprises at least one connecting via or a
plurality of connecting vias extending through said substrate from
said lower surface to said upper surface, said connecting via or
said connecting vias being at least partially filled with an
electrically conducting material, further comprising drive
circuitry, said drive circuitry electrically connected to at least
one of said anode or said cathode through said connecting via or
said connecting vias.
[0049] Preferably the drive circuitry is electrically connected to
both said anode and said cathode through said connecting via or
said connecting vias. Preferably the display device comprises a
plurality of organic diodes.
[0050] The present invention also provides a further method of
preparing an organic optoelectronic device according to the
invention comprising; [0051] providing a substrate having an upper
surface and a lower surface, said substrate further comprising at
least one connecting via or a plurality of connecting vias
extending through said substrate from said lower surface to said
upper surface, [0052] said connecting via or said connecting vias
being at least partially filled with an electrically conducting
material suitable for enabling an electrical contact to be made
between said upper surface of said substrate and said lower surface
of said substrate, [0053] providing a layer of material of high
work function over said upper surface of said substrate, [0054]
providing a layer of an organic optoelectronic material over said
layer of material of high work function, [0055] providing a layer
of transparent or semi-transparent material of low work function
over said layer of organic optoelectronic material.
[0056] Preferably the layer of material of high work function is
patterned. The layer of high work function material may be
patterned by additive techniques such as printing or by subtractive
techniques such as photolithography. The layer of high work
function material is preferably patterned to form a series of
parallel lines.
[0057] Following deposition of the layer of high work function
material it is preferred to deposit a layer of insulating material
over the layer of material of high work function and pattern said
layer of insulating material. This layer of insulating material
allows further device layers to be patterned. The layer of
insulating material may be patterned by photolithography and is
such case is preferably a photopatternable polymer. The layer of
insulating material is preferably patterned to form a series of
parallel lines which are orthogonal to the parallel lines of the
patterned material of low work function. Insulating material
patterned in this manner is known in the art as banks. Altematvely
the insulating material may be patterned to form a series of wells.
Wells are recesses in the insulating material where material has
been removed revealing the underlying layer of material of low work
function. In a more preferred embodiment a first layer of
insulating material is deposited to form a series of wells and a
second layer of insulating material is deposit over said first
layer to form a series of banks.
[0058] Preferably a patterned layer of organic optoelectronic
material is provided. The patterned layer of optoelectronic
material may be provided by subtractive or additive techniques and
preferably is provided by a selective printing technique such as
flexographic printing, gravure printing or ink-jet printing. Most
preferably the patterned layer of optoelectronic material is
provided by ink-jet printing.
[0059] Preferably said low work function material is deposited by
means of vapour deposition. It is preferred to provide a layer of
passivating material over the layer of material of low work
function. The layer of passivating material may be provided by
means of vapour deposition such as PVD or PECVD.
[0060] In the method of preparing an organic optoelectronic device
according to the present invention it is preferred that the layer
of material of low work function which forms the cathode of the
device is deposited such that it is in electrical contact with at
least one of the connecting vias, this enables both the cathode and
the anode to be electrically contacted through the vias in the
substrate. In one embodiment of the present invention prior to
providing a layer of material of low work function the organic
optoelectronic material is removed from above some of the
connecting vias allowing the layer of material of low work function
to be deposited over and in electrical contact with said connecting
via or said connecting vias. The organic optoelectronic material
may be removed, for example, by laser ablation. In an alternative
embodiment the organic optoelectronic material is selectively
deposited over the substrate such that said organic optoelectronic
material is not deposited over all of said connecting vias such
that in said step of providing a layer of material of low work
function said layer of material of low work function is deposited
over and in electrical contact with said connecting via or said
connecting vias. Methods of selective printing are preferred for
the selective deposition of the organic optoelectronic material,
ink jet printing is particularly preferred.
DETAILED DESCRIPTION OF THE INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] FIG. 1 illustrates a prior art organic electroluminescent
device on a ceramic substrate.
[0062] FIG. 2 illustrates an organic optoelectronic device
according to the present invention.
[0063] FIG. 3 shows a plurality of organic diodes on a substrate
according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0064] An optoelectronic device according to the present invention
is shown in FIG. 2. The optoelectronic device 200 comprises a
substrate 201 through which connecting vias 202 203 have been
provided. Over the upper surface of the substrate 201 and in
electrical contact with via 202 lies a layer of anode material 204.
The anode is in turn covered by a layer of organic optoelectronic
material 205 over which lies the cathode 206. An electrical
connector 207 serves to connect the cathode 206 to via 203. The
organic diode is encapsulated with a layer of passivating material
208 and the anode and cathode are connected to driving circuitry
209.
[0065] The substrate may be rigid or flexible and is generally
opaque although in some cases a transparent or semi-transparent
substrate may be used.
[0066] The substrate typically comprises a material selected from
the group comprising ceramics and plastics. The term ceramic is
taken to include both ceramics and glasses. Ceramics include high
temperature fired ceramics such as alumina, lower melting
devitrifying glasses such as are disclosed in U.S. Pat. No.
5,216,207 and low-temperature co-fired ceramic on metal composites
as disclosed in GB2263253. The substrate may be a composite
material such as a glass/plastic composite as disclosed in
EP0949850.
[0067] Suitable plastics include polyvinyl chloride, acrylonitrile
butadiene styrene (ABS), aromatic polyimides, polyimides,
propylene, polyphenylene sulfide, polycarbonate, acrylics,
polyesters, polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polyether sulfone and cyclic olefins.
[0068] The connecting vias may be through holes passing from one
surface of the substrate to the other which are filled with
conductive material or they may be formed as an integral part of
the substrate, for example as metal traces running from one surface
of the substrate to the other. Suitable materials for filling the
connecting vias include inks or pastes formed from conductive metal
particles such as copper, silver and gold combined with an organic
resin and a suitable solvent. Where the connecting vias are formed
as an integral part of the substrate they are formed from high
conductivity materials such as platinum, copper, aluminum or gold,
although molybdenum, titanium, tungsten, conductive polymers or
conductive oxides may also be used. The connecting vias will
generally have a diameter of between 5 and 100 microns and
preferably have a diameter of between 5 and 10 microns.
[0069] On the upper surface on the substrate is situated the anode
204 of the organic optoelectronic device. The anode comprises a
layer of conductive material of high work function, generally
having a work function greater than 4.3 eV. Suitable materials
include ITO, tin oxide, aluminum or indium doped zinc oxide,
magnesium-indium oxide, cadmium tin-oxide, gold, silver, nickel,
palladium and platinum. In cases where the substrate is transparent
and it is desired that light enter or leave the device through the
substrate the anode material may be transparent.
[0070] An optional layer of hole-transporting material may be
situated over the anode. The hole-transport material serves to
increase charge conduction through the device. The preferred
hole-transport material used in the art is a conductive organic
polymer such as polystyrene sulfonic acid doped polyethylene
dioxythiophene (PEDOT:PSS) as disclosed in WO98/05187, although
other hole transporting materials such as doped polyaniline or TPD
(N,N'-diphenyl-N,N'-bis(3-methylphenyl)[1,1'-biphenyl]-4,4'-diamine)
may also be used.
[0071] The nature of the organic optoelectronic material to a large
extent determines the function of the device. The preferred organic
optoelectronic devices of the present invention are organic
electroluminescent devices and organic photovoltaic devices. In
organic electroluminescent devices the optoelectronic material
comprises an organic electroluminescent material. Suitable organic
electroluminescent materials include polymeric light emitting
materials, such as disclosed in Bernius et al Advanced Materials,
2000, 12, 1737, low molecular weight light emitting materials such
aluminum trisquinoline, as disclosed in U.S. Pat. No. 5,294,869,
light emitting dendrimers as disclosed in WO99/21935 or
phosphorescent materials as disclosed in WO00/70655. The light
emitting material may comprise a blend of a light emitting material
and a fluorescent dye or may comprise a layered structure of a
light emitting material and a fluorescent dye. Due to their
processibility soluble light emitting materials are preferred, in
particular soluble light-emitting polymers. Light emitting polymers
include polyfluorene, polybenzothiazole, polytriarylamine,
poly(phenylenevinylene) and polythiophene. Preferred light emitting
polymers include homopolymers and copolymers of
9,9-di-n-octylfluorene (F8), N,N-bis(phenyl)-4-sec-butylphenylamine
(TFB) and benzothiadiazole (BT). A layer of electron transporting
or hole blocking material may be positioned over the layer of light
emitting material if required to improve device efficiency.
[0072] In organic photovoltaic devices the optoelectronic material
comprises an organic photoconductive material. Organic
heterojunction photovoltaic devices are currently one of the most
efficient types of organic photovoltaic devices. Organic
heterojunction photovoltaic devices comprise an organic electron
donor and an organic electron acceptor, such devices are disclosed
in U.S. Pat. No. 5,331,183. A variety of structures of the organic
photovoltaic devices are possible. The electron donor and electron
acceptor may comprise polymers or low molecular weight compounds.
The electron donor and acceptor may be present as two separate
layers, as disclosed in WO99/49525, or as a blend or so called bulk
heterojunction, as disclosed in U.S. Pat. No. 5,670,791. The
electron donor and acceptor may be selected from perylene
derivatives such as N,N'-diphenylglyoxaline-3,4,9,10-perylene
tetracarboxylic acid diacidamide, fullerenes (C.sub.60), fullerene
derivatives and fullerene containing polymers and semiconducting
organic polymers such as polyfluorenes, polybenzothiazoles,
polytriarylamines, poly(phenylenevinylenes), polyphenylenes,
polythiophenes, polypyrroles, polyacetylenes, polyisonaphthalenes
and polyquinolines. Preferred polymers include MEH-PPV
(poly(2-methoxy, 5-(2'-ethyl)hexyloxy-p-phenylenevinylene)),
MEH-CN-PPV
(poly(2,5-bis(nitrilemethyl)-1-methoxy-4-(2'-ethyl-hexyloxy)
benzene-co-2,5-dialdehyde-I-methoxy4-(2'-ethylhexyloxy)benzene))
and CN-PPV cyano substituted PPV, polyalkylthiophenes, such as
poly(3-hexylthiophene), POPT poly(3(4-octylphenyl)thiophene) and
poly(3-dodecylthiophene), polyfluorenes, such as
poly(2,7-(9,9-di-n-octylfluorene),
poly(2,7-(9,9-di-n-octylfluorene)-benzothiadiazole) and
poly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)).
Typical device structures include a blend of
N,N'-diphenylglyoxaline-3,4,9,10-perylene tetracarboxylic acid
diacidamide and poly(3-dodecylthiophene), a layered structure
comprising a layer of MEH-PPV and a layer of C.sub.60, a blend of
MEH-PPV and C.sub.60, a layered structure comprising a layer of
MEH-CN-PPV and a layer of POPT, a blend comprising MEH-PPV and
CN-PPV and a blend comprising poly(3-hexylthiophene) and
poly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)).
[0073] An advantage of the present invention is that the connecting
vias allow electrical contact to be made to the anode and cathode
of the diode through the substrate rather than around the sides of
the substrate. Forming the connection between anode and connecting
via is uncomplicated as the anode is deposited directly over the
substrate and the connecting vias and can therefore be deposited in
electrical contact with the connecting vias. To connect the cathode
to the connecting vias requires that any material which has been
deposited in an earlier fabrication step such as any light emitting
polymer or hole transporting material, should be removed from above
the connecting vias with which it is intended that the cathode make
contact. This organic material may be removed by laser ablation or
any other suitable technique. Alternatively the organic materials
of device may be deposited by a selective deposition technique
whereby the organic material is not deposited over the connecting
vias with which it is intended that the cathode make contact.
Suitable selective deposition techniques include selective printing
techniques with inkjet printing being a particularly suitable
technique.
[0074] The cathode 206 overlies the layer of organic optoelectronic
material. In the device of the present invention the cathode is
transparent or semi-transparent. A transparent cathode will have
greater than 80% light transmission, a semi-transparent cathode
will have a light transmission of 20 to 80%. As explained above the
use of the transparent cathode in the present invention allows the
optoelectronic device to emit or receive light through the cathode
rather than through the anode as occurs in prior art devices. This
architecture allows the cathode to be deposited as the last step in
the formation of the device with the cathode being deposited such
that it is already in contact with the connecting via or such that
it may be connected by an additional connector such as feature 207
in FIG. 2, this additional connector may be deposited using a
vapour deposition process. As described above the substrate and the
other layers of the device are prepared such that the cathode or
the additional connector form an electrical connection with the
appropriate connecting vias on deposition. Since there is no
requirement for the connecting vias to be filled when in contact
with the cathode or for the cathode to be bonded to the conductive
vias using a conductive paste or solder, the cathode is not exposed
to deleterious material.
[0075] The transparent cathode is typically formed from a thin
layer of metal having a low work function situated next to the
organic optoelectronic material. This layer provides for the
injection of electrons into the organic material or, in the case of
an organic photovoltaic device, for the collection of electrons. A
further layer of conductive material overlies the thin metal layer,
this is generally a thicker layer of a less conductive, transparent
material. Metals suitable for the thin layer of low work function
material include Ca, Ba, Mg, MgAl, LiAl, MgAg. This layer has a
thickness of between 1 nm and 30 nm, preferably 5 nm and 20 nm.
Materials suitable for the further layer of conducting material
include ITO, Al, Ag, IZO, ZnS. This layer has a thickness of
between 1 nm and 20 nm, preferably 1 nm to 10 nm.
[0076] A thin layer of insulating material is often provided
between the organic layer and the thin layer of low work function
material. This insulating material serves to improve device
efficiency by enhancing the electron transport across the
metal/organic interface. The insulating material generally has a
thickness of between 1 nm and 10 nm. Suitable materials for the
insulating material include alkali or alkaline earth metal halides
or oxides such as LIF, NaF, MgF.sub.2, BaF.sub.2, LI.sub.2O,
BaO.
[0077] Suitable structures for the transparent cathode include a
cathode comprising; [0078] a thin layer of insulating material, a
layer of metal of low work function and a further layer of metal,
for example; [0079] BaF.sub.2/Ca/Au [0080] LiF/Ca/Au [0081]
Li.sub.2O/Ag/ITO [0082] a thin layer of insulating material, a
layer of metal and a further layer of a metal containing material,
for example; [0083] LiF/Al/MgO [0084] LiF/Al/Ag [0085] a thin layer
of insulating material and a further layer of conducting material,
for example; [0086] LiF/ITO [0087] LiF/Al [0088] Li.sub.2O/ZnS
[0089] A thin layer of metal and an overlying layer of transparent,
wide bandgap semiconductor, for example; [0090] Ca/ZnSe [0091]
MgAl/ITO
[0092] A carbide, nitride or boride of an early transition metal,
lanthanide or alkaline earth metal, for example; [0093] CaB.sub.6,
LaB.sub.6, TiC, HfC, TaC, ZrN, HfN
[0094] The cathode may be deposited such that it is directly
connected to a connecting via or, as shown in FIG. 2, an electrical
connector 207 may be deposited over the cathode to connect the
cathode to the connecting via. The electrical connector may be
deposited by vapour deposition through a suitable mask.
[0095] Following deposition of the cathode a layer of protective
material may be deposited. This layer provides mechanical
protection for the organic optoelectronic device. SiO is a suitable
protective material and is typically deposited by vapour deposition
or sputtering to a thickness of between 1 and 10 nm.
[0096] To provide environmental protection the device is then
encapsulated. Where the substrate is a ceramic encapsulation may
take the form of a glass sheet which is glass bonded to the
substrate with a low temperature frit material. To avoid the
necessity of using a glass sheet to encapsulate the device a layer
of passivating material may be deposited over the device. Suitable
barrier layers comprise a layered structure of alternating polymer
and ceramic films and may be deposited by PECVD as disclosed in
WO0036665 and U.S. Pat. No. 5,686,360. Such a barrier layer is
shown as feature 208 in FIG. 2. Alternatively the device may be
encapsulated by enclosure in a metal can.
[0097] The substrate of the present invention allows electrical
connection to be made to both anode and cathode through the
connecting vias. In order to provide a driving signal to the
display, or in the case of a photovoltaic device to draw current
from the photovoltaic diodes, suitable electronics will be attached
to the connecting vias, this is shown as driving circuitry 209.
Driving circuitry for a passive matrix display will comprise a
current source connected to the column electrodes of the display,
which are typically formed by the cathodes of the organic
electroluminescent devices and a row selector connected to the row
electrodes of the display, which are typically formed by the anodes
of the organic electroluminescent devices, a central processor will
provide a timing signal to the row selector and a data signal to
the appropriate column electrodes. The driver may be in the form of
a circuit chip attached to the lower surface of the substrate,
where the substrate is a plastic the circuit chips may be deposited
using fluidic self-assembly as disclosed in WO00/46854.
[0098] FIG. 3a) shows an implementation of the present invention in
a passive matrix display device 300. A series of parallel lines of
ITO or another suitable anode material 302 are situated upon a
ceramic substrate 301. An organic optoelectronic material is
deposited over the ITO to define the light emitting pixels of the
display 304. A cathode 303 is formed as a series of parallel lines
orthogonal to the lines of ITO. The ITO contacts connecting vias
306 running along the edge of the display. The cathode contacts
connecting vias 305 running along the top of the display. Driver
electronics are connected to the connecting vias on the underside,
or lower surface, of the substrate.
[0099] FIG. 3b) shows a cross section along line A-B through the
display of FIG. 3a). The display comprises a glass substrate 301, a
layer of ITO 302, a series of banks 309 which enable the organic
optoelectronic material to be deposited as a solution (for clarity
banks 309 are not shown in FIG. 3a)). A layer of hole transporting
material 307, such as PEDOT:PSS, lies over the ITO, a layer of
light emitting polymer 308 lies over the hole transporting material
(for clarity the hole transporting layer 307 and the light emitting
layer 308 are not shown in FIG. 3a)). A cathode 303 is deposited
over the layer of light emitting polymer. Connecting via 306 serves
to connect the ITO anode to external driver circuitry.
[0100] FIG. 3c) shows a cross section along line X-Y through the
display of FIG. 3a). The display comprises a glass substrate 301, a
layer of ITO 302, a layer of hole transporting material 307, such
as PEDOT:PSS, lies over the ITO, a layer of light emitting polymer
308 lies over the hole transporting material. A cathode 303 is
deposited over the layer of light emitting polymer. Connecting via
305 serves to connect the cathode to external driver circuitry.
[0101] Clearly it is not essential for the connecting vias to be
situated at the periphery of the substrate as shown in FIG. 3 and
the vias may be positioned in the centre of the display.
[0102] A significant advantage of the present invention is that the
substrates can be tiled together to produce larger area displays.
Since electrical connection is made to the back of the substrate,
rather than to the side, several substrates can be seamlessly tiled
together with driving electronics being connected to the back, or
lower surface, of the substrate. A tiled display may be built up
from a number of substrates each comprising a discrete passively
addressed display, in this way large area passive matrix driven
displays may be formed without the need to drive excessively large
currents through the diodes of the display. Using the present
invention it is possible to make a large area or high resolution
display without the very high cost of using active matrix
semiconductor based backplanes.
[0103] The following is a description of a preferred method of
preparing an organic electroluminescent device comprising soluble
light emitting polymers according to the present invention. This
method would also be applicable to the preparation of a variety of
other organic optoelectronic devices such as organic photovoltaic
devices.
[0104] The substrate referred to in the following description is a
low-temperature co-fired ceramic on metal composite such as that
described in WO02/23579. Clearly other substrates, such as plastic
substrates, could also be used with appropriate modifications.
[0105] The ceramic substrate 301 is coated with a layer of ITO 302
to form the anode of the eventual electroluminescent device. ITO
may be deposited by sputtering or any other suitable method known
to those in the art. The ITO layer on the substrate is then
patterned using photolithography. The layer of ITO is coated with a
photoresist, patterned, for example using a UV source and a
photomask, and developed using the appropriate developing solution.
Exposed ITO is then removed by chemical etching, leaving a
patterned layer of ITO. Typically the ITO is patterned to form a
series of parallel stripes.
[0106] A layer of photopattemable, insulating polymer such as a
polyimide or a fluorinated photoresist is then deposited onto the
patterned ITO. The photopatternable polymer may be deposited by
spin-coating, doctor blade coating or any other suitable technique.
The photopattemable polymer is patterned using conventional
photolithographic techniques, for example after deposition the
photopattemable polymer is dried, exposed to UV light through a
mask, soft baked, developed using, for example, tetramethylammonium
hydroxide, rinsed and hard baked. Preferred patterns of the
insulating polymer are those that define banks, which are one
dimensional patterns, for example parallel stripes, or wells, which
are two dimensional patterns of recesses in the insulating polymer.
Banks typically have a height of 0.5 to 10 microns and a width of
10 to 100 microns and define channels containing regions of ITO
having a width of 10 to 500 microns. Wells may have a diameter of
10 to 100 microns. FIG. 3b) shows an electroluminescent device
having a series of banks 309 between areas of light emission. For
the further processing of the device it is preferred that the banks
should have a negative wall profile. Banks having a negative wall
profile are narrower in proximity to the substrate, typically a
bank will have an upper width of around 40 microns and a lower
width of around 20 to 38 microns. Techniques for obtaining banks
with a negative wall profile are known in the art and, in the case
of a negative photoresist, involve underexposing and then
overdeveloping the photoresist. The provision of banks with a
negative wall profile is beneficial for the further processing of
the substrate, in particular banks having a negative wall profile
aid the patterned deposition of the metallic cathode. EP0969701
discloses the use of banks having a negative wall profile in the
deposition of a cathode in an organic electroluminescent device.
The choice of patterning the insulating polymer to form banks or
wells is determined by the nature of the eventual light emitting
device. If it is desired that the device emit light of a single
colour, i.e. a monochrome device, it is sufficient to pattern the
substrates with banks. If it is desired that the device emit in
more than one colour, in particular in red, green and blue, the
insulating polymer will generally be patterned to form wells, thus
enabling light emitting materials of different colours to be
deposited separately, with an additional layer of banks to
facilitate cathode deposition.
[0107] The substrate, layers of photopatternable polymer and
exposed ITO may be further surface treated for example using oxygen
plasma or ultraviolet light. This serves to alter the surface
energies of the materials of the substrate making them more
suitable for the deposition of the device layers. Surface treatment
is particularly desirable when further materials are to be
deposited by solution processing techniques.
[0108] A layer of hole-transporting material, 307 FIG. 3b), is then
deposited upon the patterned ITO. The preferred hole-transport
material used in the art is a conductive organic polymer such as
polystyrene sulfonic acid doped polyethylene dioxythiophene
(PEDOT:PSS) as disclosed in WO98/05187, although other hole
transporting materials such as doped polyaniline may also be used.
The hole-transporting material may be deposited by ink jet
printing. PEDOT:PSS may be ink-jet printed as an aqueous solution.
The aqueous solution typically has a concentration of 1 to 10% of
hole-transporting material. After deposition the aqueous solution
is allowed to evaporate leaving a layer of hole-transporting
material of thickness 10 nm to 200 nm. The PEDOT:PSS is ink-jet
printed so that the connecting vias which are intended to form a
contact with the cathode are not covered by PEDOT:PSS.
[0109] Following deposition of the hole transporting layer, a layer
of light emitting material, 308 FIG. 3b) is deposited into selected
wells on the substrate. The light emitting polymer is deposited
using ink-jet printing. Conjugated polymers such as polyfluorene
and poly(phenylene vinylene) may be ink-jet printed from solutions
of aromatic solvents such as toluene, xylene, trimethylbenzene etc.
The light-emitting polymer may be ink-jet printed from a solution
of concentration 0.5 to 10%, the thickness of the deposited layer
of light-emitting polymer is generally 10 nm to 300 nm. As above
the light emitting polymer is deposited by ink-jet printing such
that the connecting vias which are intended to form a contact with
the cathode are not covered by light emitting polymer.
[0110] In cases where the PEDOT:PSS and the light emitting polymer,
or other appropriate device materials, are deposited by
non-selective techniques, such as spin-coating or doctor blade it
may be necessary to remove the material from above the connecting
vias to which the cathode will connect. Laser ablation is a
suitable technique for the removal of excess material.
[0111] A cathode material 303 is then deposited over the light
emitting material. The cathode material is deposited by means of
vapour deposition. Where appropriate multilayer cathodes may be
deposited, for example cathodes comprising a layer of alkali or
alkaline earth metal fluorides and layers of metals as discussed
above. A particularly preferred cathode comprises LIF/Ca/Al, with a
layer of LiF of thickness from 1 to 10 nm, a layer of Ca of
thickness of 1 to 25 mm and a layer of Al of thickness 10 to 500
mm.
[0112] The device is then encapsulated, this may be carried out by
means of enclosing the device in a metal can or glass cover to
protect the device from the environment, an oxygen or moisture
absorbent may be including within the metal can or glass cover,
such a technique is disclosed in U.S. Pat. No. 6,080,031.
Alternatively devices may be encapsulated by laminating an
impermeable composite material over the device as is disclosed in
WO00/36661.
[0113] The present invention has particular application in the
field of organic light emitting devices where it enables the
production of large area displays. The present invention also has
application in the field of organic photovoltaic devices. Organic
photovoltaic devices are generally formed on glass substrates, the
use of more robust ceramic or plastic substrates as in the present
invention greatly increases the fields of application of organic
photovoltaic devices such as for the roofing or exterior cladding
of buildings. The present invention also allows organic
photovoltaic devices to be seamlessly tiled together, enabling
greater active surface coverage and allowing the devices to be
series connected to increase the voltage generation.
[0114] No doubt the teaching herein makes many other embodiments
of, and effective alternatives to, the present invention apparent
to a person skilled in the art. The present invention is not
limited to the specific embodiments described herein but
encompasses modifications which would be apparent to those skilled
in the art and lying with the spirit and scope of the attached
claims.
* * * * *